We used chemical equilibrium calculations to model thermal metamorphism of ordinary chondritic material as a function of temperature, pressure, and trace element abundance and use our results to discuss volatile mobilization during thermal metamorphism of ordinary chondrite parent bodies. The calculations include ~ 1,700 solids and gases of 40 elements. We compiled trace element abundances in H, L, and LL chondrites for the elements Ag, As, Au, Bi, Cd, Cs, Cu, Ga, Ge, In, Pb, Rb, Sb, Se, Sn, Te, Tl, and Zn, and identified abundance trends as a function of petrographic type within each class. We found that abundance patterns within the H-and L-chondrites are consistent with mobilization of volatile elements in an onionshell-type parent body. LL-chondrites have more complex abundance patterns that may support a rubble-pile model for the LLchondrite parent body. We calculated volatility sequences for the trace elements in the ordinary chondritic material, which differ significantly from the solar nebula volatility sequence.Our work addresses three important questions. First, do elemental volatilities during ordinary chondrite metamorphism differ from those during condensation in the solar nebula? This question is important because cosmochemists presently use the nebular volatility sequence to discuss metamorphic chemistry of volatile elements. C:\Laura\Ivtan\Early Earth\trace\SF08trace.doc 4:39:13 PM 1/4/2008 5 Second, does thermal metamorphism affect the abundances and chemistry of volatile elements in ordinary chondrites? Third, do volatile element abundances vary inside thermally metamorphosed asteroids?We focus on carbon and volatile trace elements (Ag, As, Au, Bi, Cd, Cs, Cu, Ga, Ge, In, Pb, Rb, Sb, Se, Sn, Te, Tl, Zn) in this paper for two reasons. First, thermal metamorphism was isochemical with respect to the major rock-forming elements such as Ca, Mg, Al, Si, Fe, and Ti (McSween et al., 1988). Second, Schaefer and Fegley (2007a) found that the abundances of F, Cl, and S, which are also volatile elements, are unaltered by thermal metamorphism. These elements are mainly in minerals throughout the range of metamorphic temperatures instead of being in the gas phase.Our paper is organized as follows. Section 2 gives background information on ordinary chondrites and thermal metamorphism. Section 3 discusses the trace element abundances in H-, L-, and LL-chondrites and abundance trends as a function of petrologic type. Section 4 describes our thermodynamic calculations. In Section 5, we discuss the results of our thermodynamic calculations for the trace elements. We take our discussion of carbon from Schaefer and Fegley (2007a), who discuss results for 20 major and minor elements. In section 6, we describe the calculated volatility sequence and compare it to solar nebular volatility and trace element mobility in ordinary chondrites.We also discuss, using our results, possible mechanisms for producing the observed trends in the trace element abundances. Section 7 gives our answers to the questions posed in the i...